It is well known that inaccuracies are often introduced into spectrometric analyses by the photoconductive detectors employed, due to nonlinearity between the electrical signal generated and the energy of the incident radiation.
A method and apparatus for correcting such nonlinearity are disclosed in Keens et al U.S. Pat. No. 4,927,269, issued May 22, 1990. Because it is predicated upon a series of somewhat arbitrary assumptions, however, the technique described by Keens et al is believed to be of only limited utility and value.
A highly effective method for correction of such detector nonlinearity, and a system implementing the same, are described and claimed in Carangelo et al U.S. Pat. No. 5,136,154. In accordance with the method thereof, a photoconductive detector, to which is applied a constant bias voltage, is used to generate an electrical signal having a time-varying value X.sub.s, the value X.sub.s being indicative of the energy of electromagnetic radiation incident upon the detector but including distortions which render it nonlinearly related thereto. A corrective signal is produced having the value (X.sub.s -C).sup.2, at least a fraction of which is added to a signal having at least the value X.sub.s so as to substantially eliminate the distortions and thereby produce a linearized output signal.
In applying the Carangelo et al method, the generated and corrective signals are generally combined in accordance with the relationship: EQU 1/a.times.(X.sub.s +f[X.sub.x -C].sup.2),
wherein "f" is a fractional constant and "a" has a value of either unity (when X.sub.s is detector output voltage), or of "f" (when X.sub.s is the A.C. portion of a modulated signal). A specific value "f.sub.o " of the constant "f" is established at which, in the combined signal, the electrical distortions are substantially eliminated.